1. Introduction to Database
CHAPTER 4
Advanced SQL
SQL Data Types and Schemas
Integrity Constraints
Authorization
Embedded SQL
Dynamic SQL
Functions and Procedural Constructs**
Recursive Queries**
Advanced SQL Features**

2. 4.1 SQL Data Types and Schemas
Basic Data Types:
Integer
Char …
Build-in Data Types in SQL
User-Defined Types
Large-Object Types

3. 4.1.1 Build-in Data Types in SQL
date: Dates, containing a (4 digit) year, month and date, ‘ ’
time: Time of day, in hours, minutes and seconds, ‘09:00:30’
timestamp: date plus time of day, ‘ :00:30.75’
Operations for Build-in Data Types in SQL :
Convert string types to date/time/timestamp, cast string as date
Find interval: period of time, dtae1 – date2
Interval values can be added to date/time/timestamp values
Extract values of individual fields from date/time/timestamp
Example: extract (year from r.starttime)
Comparison: if date1 < date2 then …

4. 4.1.2 User-Defined Types
create type: construct in SQL creates user-defined type
E.g. create type Dollars as numeric (12,2) final
create domain: construct in SQL-92
E.g. create domain person_name char(20) not null
Types and domains are similar.
Domains can have constraints, such as not null, specified on them.
v.s.
create string person_name char(20); 整

5. Domain Constraints Domain constraints
are the most elementary form of integrity constraint.
They test values inserted in the database,
and test queries to ensure that the comparisons make sense.
We cannot assign or compare a value of type USDollar to a value of type NTDollar.
However, we can convert type as below (cast r.A*32.5 as NTDollar) //conversion-rate

6. 4.1.3 Large-Object Types
Large objects (photos, videos, CAD files, etc.) are stored as a large object:
blob: binary large object –
object is a large collection of uninterpreted binary data
whose interpretation is left to an application outside of the database system
clob: character large object –
object is a large collection of character data
When a query returns a large object,
a pointer is returned rather than the large object itself.

7. 4.1.4 Schemas, Catalogs, and Environments
Naming Relations: three-level hierarchy for naming relations.
Database: contains multiple catalogs
Catalog: can contain multiple schemas
Schemas: can contain many relations and views
e.g. catalog5.bank-schema.account
Each user has a default catalog and schema, and the combination is unique to the user.
Default catalog and schema are set up for a connection
Catalog and schema can be omitted, defaults are assumed
Multiple versions of an application (e.g. production and test) can run under separate schemas

8. 4.2 Integrity Constraints
guard against accidental damage to the database,
by ensuring that authorized changes to the database do not result in a loss of data consistency.
Example:
E.g. 1: A checking account must have a balance greater than $10,000.00
E.g. 2: A salary of a bank employee must be at least $4.00 an hour
E.g. 3: A customer must have a (non-null) phone number

9. 4.2.1 Constraints on a Single Relation
not null
primary key
unique
check (P ), where P is a predicate
create table branch (branch-name char(15) not null, branch-city char(30), assets integer, primary key (branch-name), check (assets >= 0))

10. 4.2.2 Not Null Constraint
E.g. Declare branch_name for branch is not null
branch_name char(15) not null
E.g. Declare the domain Dollars to be not null
create domain Dollars numeric(12,2) not null
create table branch (branch-name char(15) not null, branch-city char(30), assets integer, primary key (branch-name), check (assets >= 0))

11. 4.2.3 Unique Constraint A statement: unique ( A1, A2, …, Am)
The unique specification states that the attributes
A1, A2, … Am
form a candidate key.

12. 4.2.4 The check clause check (P ), where P is a predicate
Example 1: Declare branch_name as the primary key for branch and ensure that the values of assets are non-negative.
attribute
create table branch (branch-name char(15) not null, branch-city char(30), assets integer, primary key (branch-name), check (assets >= 0))
Example 2: Use check clause to ensure that an hourly_wage domain allows only values greater than a specified value.
create domain hourly_wage numeric(5,2) constraint value_test check(value > = 4.00)
The clause constraint value_test is optional
Domain

13. 4.2.5 Referential Integrity
Referential Integrity: ensures that a value that appears in one relation for a given set of attributes also appears for a certain set of attributes in another relation.
Example: If “Perryridge” is a branch-name appearing in one of the tuples in the account relation, then there exists a tuple in the branch relation for branch “Perryridge”.
In SQL create table statement:
The primary key clause: lists attributes that comprise the primary key.
The unique key clause: lists attributes that comprise a candidate key.
The foreign key clause: lists the attributes that comprise the foreign key and the name of the relation referenced by the foreign key.

14. Referential Integrity: Example
create table account (account-number char(10), branch-name char(15), balance integer,
primary key (account-number),
foreign key (branch-name) references branch)
3. account
1. branch

15. Referential Integrity in SQL
Foreign keys can be specified as part of the SQL create table statement:
By using the foreign key clause
By default, a foreign key references the primary key attributes of the referenced table
create table account (account-number char(10), branch-name char(15), balance integer,
primary key (account-number),
foreign key (branch-name) references branch)

16. Example: Banking Database
Banking Database: consists 6 relations:
branch (branch-name, branch-city, assets)
customer (customer-name, customer-street, customer-only)
account (account-number, branch-name, balance)
loan (loan-number, branch-name, amount)
depositor (customer-name, account-number)
borrower (customer-name, loan-number)

17. Example: Banking Database
1. branch
2. customer
3. depositor
存款戶
分公司
客戶(存款戶,貸款戶)
4. borrower
貸款戶
5. account
存款帳
6. loan
貸款帳

18. Referential Integrity in SQL: Example
2. customer
create table customer (customer-name char(20), customer-street char(30), customer-city char(30), primary key (customer-name))
create table branch (branch-name char(15), branch-city char(30), assets integer, primary key (branch-name))
1. branch

19. Referential Integrity in SQL: Example (cont.)
5. account
存款帳
create table account (account-number char(10), branch-name char(15), balance integer,
primary key (account-number),
foreign key (branch-name) references branch)
create table depositor (customer-name char(20), account-number char(10),
primary key (customer-name, account-number),
foreign key (account-number) references account,
foreign key (customer-name) references customer)
3. depositor
references
存款戶

20. GQBE: Query Example
Example query: Find the customer-name, account-number and balance for all accounts at the Perryridge branch

21. Referential Integrity: Cascade
5. account
create table account
(account-number char(10), branch-name char(15), balance integer, primary key (account-number), foreign key (branch-name) references branch) on delete cascade
on update cascade )
references
1. branch
Due to the on delete cascade clauses,
if a delete of a tuple in branch
Eg. Brighton Broklyn
the delete “cascades” to the account relation, A-201, A-217
Cascading updates are similar.
See p.130

22. Referential Integrity: Set Null
5. account
create table account
(account-number char(10), branch-name char(15), balance integer, primary key (account-number), foreign key (branch-name) references branch) on delete set null )
null
null
references
1. branch
Due to the on delete set null clauses,
if a delete of a tuple in branch
Eg. Brighton Broklyn
the delete “set null” to the account relation, A-201, A-217

23. 4.2.6 Assertions/Integrity Rules
主張, 宣告
4.2.6 Assertions/Integrity Rules
An assertion is a predicate expressing a condition that we wish the database always to satisfy.
An assertion in SQL takes the form
create assertion <assertion-name> check <predicate>
E.g. create assertion balance-constraint check account.balance >= 1000
When an assertion is made, the system tests it for validity, and tests it again on every update that may violate the assertion
The testing may introduce a significant amount of overhead;
Hence, assertions should be used with great care.
The rule of an assertion is stored in “dictionary” (system catalog)

24. 0.2 Architecture for a Database System View 2: Three Tiers
Host
Language
+ DSL
User A1
User A2
User B1
User B2
User B3
External View
@ # & B
External/conceptual
mapping A
Conceptual
View
mapping B
Conceptual/internal
mapping
Stored database (Internal View)
Database
management
system Dictionary
(DBMS) e.g. system
catalog
<
DBA
Storage
structure
definition
(Internal
schema)
schema
External A
(Build and
maintain
schemas
and
mappings) # @
&
DSL (Data Sub. Language)
C, C++
e.g. SQL 1 2 3
...
100

25. Assertion: Example 1
The sum of all loan amounts for each branch must be less than the sum of all account balances at the branch.
create assertion sum-constraint check (not exists (select * from branch where (select sum(amount) from loan where loan.branch-name = branch.branch-name) >= (select sum(amount) from account where loan.branch-name = branch.branch-name)))

26. Assertion: Example 2
Every loan has at least one borrower who maintains an account with a minimum balance or $
create assertion balance-constraint check (not exists ( select * from loan where not exists ( select * from borrower, depositor, account where loan.loan-number = borrower.loan-number and borrower.customer-name = depositor.customer-name and depositor.account-number = account.account-number and account.balance >= 1000)))

27. 4.3 Authorization Forms of authorization on parts of the database:
Read authorization
Insert authorization
Update authorization
Delete authorization
Forms of authorization to modify the database schema:
Index authorization - allows creation and deletion of indices.
Resources authorization - allows creation of new relations.
Alteration authorization - allows addition or deletion of attributes in a relation.
Drop authorization - allows deletion of relations.

28. Authorization Specification in SQL
The grant statement is used to confer authorization
< privilege list> is: select, insert, update, delete, all privileges, … (ch. 8)
<user list> is:
a user-id
public, which allows all valid users the privilege granted
A role (ch. 8)
E.g.
The grantor of the privilege must already hold the privilege on the specified item (or be the database administrator).
grant <privilege list> on <relation name/view name> to <user list>
grant select on branch to U1, U2, U3

29. Revoking Authorization in SQL
The revoke statement is used to revoke authorization.
Example:
revoke select on branch from U1, U2, U3
revoke <privilege list> on <relation name or view name> from <user list>

30. 4.4 Embedded SQL
Embedded SQL: The SQL standard defines embeddings of SQL in a variety of programming languages such as Pascal, PL/I, Fortran, Cobol, C, C++, C#, and Visual Basic.
Host language: A language to which SQL queries are embedded is referred to as a host language.
The basic form of these languages follows that of the System R embedding of SQL into PL/I.
EXEC SQL statement is used to identify embedded SQL request to the preprocessor
Note: This varies by language. e.g. the Java embedding uses
EXEC SQL <embedded SQL statement > END-EXEC
# SQL { …. } ;

31. Embedded SQL: Example
Example: From within a host language, find the names and cities of customers with more than the variable amount dollars in some account.
Specify the query in SQL and declare a cursor for it
EXEC SQL
declare c cursor for select customer-name, customer-city from depositor, customer, account where depositor.customer-name = customer.customer-name and depositor account-number = account.account-number and account.balance > :amount
END-EXEC

32. Embedded SQL (cont.)
The open statement causes the query to be evaluated
EXEC SQL open c END-EXEC
The fetch statement causes the values of one tuple in the query result to be placed on host language variables.
EXEC SQL fetch c into :cn, :cc END-EXEC Repeated calls to fetch get successive tuples in the query result
A variable called SQLSTATE in the SQL communication area (SQLCA) gets set to ‘02000’ to indicate no more data is available
The close statement causes the database system to delete the temporary relation that holds the result of the query.
EXEC SQL close c END-EXEC
Note: above details vary with language. E.g. the Java embedding defines Java iterators to step through result tuples.

33. Updates Through Cursors
Can update tuples fetched by cursor by declaring that the cursor is for update
To update tuple at the current location of cursor
declare c cursor for select * from account where branch-name = ‘Perryridge’ for update
update account set balance = balance where current of c

34. 4.5 Dynamic SQL Dynamic SQL:
Allows programs to construct and submit SQL queries at run time.
Note: Embedded SQL – at compile time
Program creates SQL queries as stings at run time (perhaps based on input from the user)
Can either have them executed immediately or have them prepared for subsequent use
Example: dynamic SQL in a C program char * sqlprog = “update account set balance = balance * where account-number = ?” EXEC SQL prepare dynprog from :sqlprog; char account [10] = “A-101”; EXEC SQL execute dynprog using :account;

35. Dynamic SQL (cont.)
The dynamic SQL program contains a ?, which is a place holder for a value that is provided when the SQL program is executed.
Two major Connectivity:
ODBC (Open Database Connectivity) works with C, C++, C#, and Visual Basic
JDBC (Java Database Connectivity) works with Java
SQL Session
When a user/application program connects to an SQL sever, a session is established
Executes statements on the session
Disconnects the session finally
Buffer

36. 4.5.1 ODBC Open DataBase Connectivity (ODBC) standard
Defines a way for application a program to communicate with a database server.
ODBC defines an API (Application Program Interface) that applications can use to
open a connection with a database,
send queries and updates,
get back results.
Applications such as
GUI (graphical user interfaces), spreadsheets, etc.
can use of the same ODBC API to connect to any database server that supports ODBC
ODBC Code Example
Fig. 4.4, p.139

37. Client/Server Architecture (補)
Applications
DBMS
ODBC API call
driver library
Client machine
Server machine
Fig: A client/server system
some sites are client, and others are server sites
a great deal of commercial products
little in "true" general-purpose distributed system (but long-term trend might be important)
client: application or front-end
server: DBMS or backend
Several variations

38. ODBC (cont.)
Each database system supporting ODBC provides a "driver" library that must be linked with the client program.
When client program makes an ODBC API call, the code in the library communicates with the server to carry out the requested action, and fetch results.
ODBC program first allocates
an SQL environment: HENV env;
a database connection handle: HDBC conn;
Opens database connection using SQLConnect( ). Parameters are:
connection handle: conn
the server to which to connect: “db.yale.edu”
the user identifier: “avi”
Password: “avipasswd”
Must also specify types of arguments:
SQL_NTS denotes previous argument is a null-terminated string.

39. ODBC Code int ODBCexample() { RETCODE error;
HENV env; /* environment */
HDBC conn; /* database connection */
SQLAllocEnv(&env);
SQLAllocConnect(env, &conn);
SQLConnect(conn, "aura.bell-labs.com", SQL_NTS, "avi", SQL_NTS, "avipasswd", SQL_NTS);
SQLDisconnect(conn);
SQLFreeConnect(conn);
SQLFreeEnv(env); }
{ …. Do actual work … } // Main body of program

40. ODBC Code (cont.) Main body of program
char branchname[80]; float balance; int lenOut1, lenOut2; HSTMT stmt;
char * sqlquery = "select branch_name, sum (balance) from account group by branch_name";
SQLAllocStmt(conn, &stmt); error = SQLExecDirect(stmt, sqlquery, SQL_NTS); //sends SQL to the database
if (error == SQL_SUCCESS) { SQLBindCol(stmt, 1, SQL_C_CHAR, branchname, 80, &lenOut1); SQLBindCol(stmt, 2, SQL_C_FLOAT, &balance, 0, &lenOut2);
while (SQLFetch(stmt) == SQL_SUCCESS) { printf (" %s %g\n", branchname, balance); } } SQLFreeStmt(stmt, SQL_DROP);

41. ODBC Code (cont.)
SQLExecDirect: Program sends SQL commands to the database
SQLFetch(): Result tuples are fetched using SQLFetch()
SQLBindCol(): binds C language variables to attributes of the query result
When a tuple is fetched, its attribute values are automatically stored in corresponding C variables.
Arguments to SQLBindCol()
ODBC stmt variable, attribute position in query result
The type conversion from SQL to C.
The address of the variable.
variable-length types
Feedback:
Good programming requires checking results of every function call for errors;
we have omitted most checks for brevity.

42. More ODBC Features Prepared Statement
SQL statement prepared: compiled at the database
Can have placeholders: E.g. insert into account values(?,?,?)
Repeatedly executed with actual values for the placeholders
Metadata features
finding all the relations in the database and
finding the names and types of columns of a query result or a relation in the database.
By default, each SQL statement is treated as a separate transaction, that is committed automatically.
Can turn off automatic commit on a connection
SQLSetConnectOption(conn, SQL_AUTOCOMMIT, 0)}
transactions must then be committed or rolled back explicitly by
SQLTransact(conn, SQL_COMMIT) or
SQLTransact(conn, SQL_ROLLBACK)

43. ODBC Conformance Levels
Conformance levels specify subsets of the functionality defined by the standard.
Core
Level 1 requires support for metadata querying
Level 2 requires ability to send and retrieve arrays of parameter values and more detailed catalog information.
SQL Call Level Interface (CLI) standard similar to ODBC interface, but with some minor differences.

44. 4.5.2 JDBC
JDBC is a Java API for communicating with database systems supporting SQL
JDBC supports a variety of features for querying and updating data, and for retrieving query results
JDBC also supports metadata retrieval, such as querying about relations present in the database and the names and types of relation attributes
Model for communicating with the database:
Open a connection
Create a “statement” object
Execute queries using the Statement object to send queries and fetch results
Exception mechanism to handle errors
JDBC Code Example
Fig. 4.5, p.141

45. JDBC Code { …. Do actual work … } // Main body of program
public static void JDBCexample(String dbid, String userid, String passwd) {
try {
Class.forName ("oracle.jdbc.driver.OracleDriver"); //load drivers
Connection conn =DriverManager.getConnection( userid, passwd);
Statement stmt = conn.createStatement(); //create a statement handle .
stmt.close();
conn.close(); //disconnect }
catch (SQLException sqle) {
System.out.println("SQLException : " + sqle); //print out error message
//get connection
{ …. Do actual work … } // Main body of program

46. JDBC Code (Cont.) Update to database
try {
stmt.executeUpdate( "insert into account values ('A-9732', 'Perryridge', 1200)");
} catch (SQLException sqle) {
System.out.println("Could not insert tuple. " + sqle); }
Execute query and fetch and print results
ResultSet rset = stmt.executeQuery( "select branch_name, avg(balance) from account group by branch_name");
while (rset.next()) {
System.out.println( rset.getString("branch_name") + " " + rset.getFloat(2));
//update
//get error message
//print out error message
//retrieve a result set
//retrieve next tuple on the result set one by one
//print out error message

47. JDBC Code Details Getting result fields:
rs.getString(“branchname”) and rs.getString(1)
equivalent if branchname is the first argument of select result.
Dealing with Null values
int a = rs.getInt(“a”);
if (rs.wasNull()) Systems.out.println(“Got null value”);

48. Prepared Statement
Prepared statement allows queries to be compiled and executed multiple times with different arguments:
PreparedStatement pStmt = conn.prepareStatement(
“insert into account values(?,?,?)”); pStmt.setString(1, "A-9732");
pStmt.setString(2, "Perryridge");
pStmt.setInt(3, 1200);
pStmt.executeUpdate();
pStmt.setString(1, "A-9733");